The flexibility and convenience of battery powered tools has led to remarkable growth in the number and operational range of battery powered tools such as drills, sanders, saws and routers. Purchasers of these tools, which are often sold in kits containing several different tools and multiple battery packs and a device for recharging exhausted or rundown battery packs, are motivated by the freedom that battery powered tools provide.
Despite their convenience, battery powered tools as presently marketed have a number of limitations. The increasing demand for power delivering capability of these battery powered tools has prompted physically larger, heavier, larger capacity battery packs. Despite the larger capacity battery packs, power demanding tool usage rapidly depletes the energy source requiring frequent battery pack changes and recharging. Equally important, the power tool's full rated torque is only achieved when the tool motor is fed full voltage and current and this torque is only achieved with a new fully charged battery and as a result the delivered torque of the battery powered tool decreases not only as the battery energy is depleted between charges, but also decreases by the number of battery charging cycles.
The charger device capability has also kept up with demand such that battery packs can be recharged in an hour or less. With heavy usage of a power demanding battery tool such as a saw or hammer drill, the user often must change and recharge the tool's battery packs within an hour or less usage time. Additionally, demanding usage of the battery packs causes excessive battery heat buildup requiring the packs to cool down before being recharged.
As a result, users of battery powered tools often purchase multiple battery packs and chargers and must work near a source of AC mains power for the chargers. Additionally, users purchase AC mains powered tools to supplement their battery powered tools during periods of battery recharging and when the job requires a tool with constant full torque.